1. Field
The presently disclosed subject matter relates to a semiconductor light source apparatus and a lighting unit using the semiconductor light source apparatus, and more particularly to a high power semiconductor light source apparatus including a phosphor layer that can prevent a reduction of brightness caused by thermal quenching and a lighting unit that can also emit various color lights having a substantially uniform color tone and a large amount of light intensity that can be used for general lighting, such as a stage light, a street light, or a vehicle lamp such as a headlight, etc.
2. Description of the Related Art
Semiconductor light source apparatuses that emit various color lights by combining a phosphor layer with a semiconductor light-emitting device such as an LED have been popularly used for various fields. Recently, because brightness of the semiconductor light source apparatuses has improved, the range of applications for semiconductor light source apparatuses has expanded to fields such as general lighting, vehicle headlight, etc. Such light source apparatuses may become popular for additional uses in the future due to its improved brightness characteristics.
One conventional method for improving the brightness of semiconductor light source apparatuses which combine the phosphor layer with the semiconductor light-emitting device may include enhancing the excitation intensity of the phosphor layer by flowing a large current in the semiconductor light-emitting device. However, because heat is generated in the phosphor layer due to the large current, the transparent resin may be tarnished, especially when the transparent resin achieves high temperatures of more than 200 degrees Celsius. Because the transparent resin is mixed in the phosphor layer, the tarnish of the transparent resin results in absorption of a part of light excited by the phosphor layer, and therefore may cause a reduction of the excitation intensity.
In addition, a reduction of fluorescent intensity may be caused by a thermal quenching property of the phosphor layer due to the large current. The thermal quenching property is a phenomenon in which a fluorescent intensity of a phosphor becomes reduced when the phosphor is heated at a high temperature. Therefore, because the tarnish of the transparent resin and the reduction of the fluorescent intensity cause a reduction of a light intensity in semiconductor light source apparatuses that include a phosphor layer, it is difficult to improve the brightness of the semiconductor light source apparatuses by simply flowing a larger current.
To address this problem, a semiconductor light source apparatus using a phosphor layer that includes a phosphor particle without a transparent resin is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2006-005367). FIG. 14 is a schematic structural view showing a conventional semiconductor light source apparatus including a phosphor layer, which is disclosed in Patent Document No. 1.
The conventional semiconductor light source apparatus includes a semiconductor light-emitting device 95 and a phosphor ceramic layer 92 including a phosphor particle without a transparent resin. The phosphor ceramic layer 92 may not include a transparent resin, and therefore tarnish of the phosphor ceramic layer 92 may not occur. In addition, because the phosphor ceramic layer 92 is made of a material having a low thermal sensitivity, thermal quenching may be prevented. Consequently, it may be possible for this semiconductor light source apparatus to improve brightness by simply flowing a large current therethrough.
However, in the conventional semiconductor light source apparatus, after light emitted from the semiconductor light-emitting device 95 is wavelength-converted via the phosphor ceramic layer 92, the light is emitted in the opposite direction of the semiconductor light-emitting device 95. Accordingly, light reflected on the phosphor ceramic layer 92 from the light emitted from the semiconductor light-emitting device 95 may return to the semiconductor light-emitting device 95 and may be absorbed in the semiconductor light-emitting device 95. The reflected light may cause a reduction of light use efficiency.
Moreover, heat generated from the phosphor ceramic layer 92 may be transmitted to the semiconductor light-emitting device 95 and may be radiated from a mounting substrate, on which the semiconductor light-emitting device 95 is mounted. However, because the semiconductor light-emitting device 95 also generates heat, the radiating efficiency of the semiconductor light source apparatus may not be high.
As described above, the conventional semiconductor light source apparatus is a light transmission type apparatus, which emits a wavelength converted light by passing light emitted from the light-emitting device 95 through the phosphor ceramic layer 92 that is located on the light-emitting device 95. In such a semiconductor light source apparatus, it may be difficult to improve a radiating efficiency of the phosphor ceramic layer 92, and therefore there may be limitations in super high-intensity lighting.
Accordingly, another conventional semiconductor light source apparatus of a reflection type is disclosed in Patent Document No. 2 (U.S. patent application Ser. No. 12/972,056 filed on Dec. 17, 2010) by applicant of the present application. FIGS. 15a and 15b are a schematic front view and a top view showing the other conventional semiconductor light source apparatus of the reflection type, which is disclosed in Patent Document No. 2.
The semiconductor light source apparatus 100 includes a solid state light source 105, and a phosphor layer 102 located away from the solid state light source 105, the phosphor layer 102 receiving excitation light emitted from the light source 105 and reflecting/emitting a wavelength converted light, which mixes light having a wavelength emitted from the phosphor layer 102 by absorbing a part of the excitation light emitted from the light source 105 through the phosphor layer 102 with another part of the excitation light that is not excited by the phosphor layer 102.
The phosphor layer 102 is located on a radiating substrate 106 via a reflective adhesive layer 107. The semiconductor light source apparatus 100 may efficiently reflect fluorescence having a different wavelength emitted from the phosphor layer 102 from that of the excitation light emitted from the light source 105 and the other part of the excitation light by using at least one of the reflective adhesive layer 107 and the radiating substrate 106. Therefore, the reflective type structure, in which the phosphor layer 102 does not contact with the light source 105, may allow the semiconductor light source apparatus 100 to emit light having the super high-intensity because the radiating efficiency of the phosphor layer 102 and the light source 105 can easily improve.
However, in the reflection type structure in which the phosphor layer 102 is located away from the light source 105, for example when a yellow phosphor such as YAG is used as the phosphor layer 102 and a blue LED is used as the light source 105, and when the semiconductor light source apparatus projects a wavelength converted light using a yellow fluorescent and a blue excitation light on a projection plane, for example, via a diffusing lens, the wavelength converted light projected on the projection plane may be subject to a light-emitting color variability.
FIG. 16 is an explanatory drawing for explanting the light-emitting color variability, which may be caused by the reflective type conventional light source apparatus. The conventional semiconductor light source apparatus 100 may include light having a substantially white color tone by an additive color mixture of the yellow fluorescent light emitted from the phosphor layer 102 and the blue excitation light emitted from the light source 105.
However, when a part of the blue excitation light is mirror-reflected on a top surface of the phosphor layer 102 as shown by an arrow in FIG. 16, the part of the blue excitation light may be projected as an enlarged blue light 171 on the projection plane 170 via a diffusing lens 115 as shown in FIG. 16. Hence, the enlarged blue light 171 may be projected as the light-emitting color variability on the light having a substantially white color tone, which is essentially emitted from the conventional semiconductor light source apparatus. As a result, the conventional semiconductor light source apparatus 100 may emit a wavelength converted light having little light-emitting color variability.
The above-referenced Patent Documents are listed below and are hereby incorporated with their English abstracts in their entireties.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2006-005367    2. Patent document No. 2: U.S. application Ser. No. 12/972,056 filed on Dec. 17, 2010 and owned by Applicant of the present application.
The disclosed subject matter has been devised to consider the above and other problems, characteristics and features. Thus, an embodiment of the disclosed subject matter can include semiconductor light source apparatuses which can emit various color light having a substantially uniform color tone and high brightness and can efficiently radiate heat even when a high power semiconductor light-emitting device is used under a large current as a light source. In this case, an excitation light emitted from a high power semiconductor light-emitting device can be efficiently wavelength-converted by a phosphor layer without a mirror reflection on the phosphor layer and a reduction of light intensity, because the phosphor layer is located on a radiating substrate and does not include a substantially resin component and because the excitation light can enter into the phosphor layer so as not to be mirror-reflected on the phosphor layer.